It sure is substantial, but what does that have to do with anything?
The Public Service Loan Forgiveness program was passed in 2007 by Congress and signed by President Bush. You're accusing him of forgiving loans without Congressional approval. That's simply false.
IDR repayment programs have been around for decades and amended numerous times.
All the programs you mentioned in this quote have explicit legislative authorization. The "major decisions" doctrine simply doesn't apply.
This isn't a loophole. This is just the Biden administration taking a system that was dysfunction and ignored and making it work for people who qualified for loan forgiveness.